The invention relates to the field of analog to digital (A/D) converters in which an unknown analog voltage is represented by a digital signal equivalent. Many forms of such converters have been developed to act as the interface between digital computers and the analog outputs of transducers that measure the various parameters of the physical environment. Integrating A/D converters employ the integral of the analog voltage over a conversion internal as the digital equivalent. These are usually of the dual slope variety. Kelly U.S. Pat. No. 3,958,236 shows one such dual slope A/D converter with means for injecting an offset voltage having a magnitude and polarity that will correct for drift and offset. Neelands U.S. Pat. No. 3,555,298 shows an A/D converter that employs a capacitor charged to the analog voltage and then discharged through a constant current circuit to provide a linear ramp. A comparator terminates the ramp when a reference potential is reached. The device is alternately supplied with unknown and reference potentials and a corrected digital readout indicates the unknown quantity. Balcom, Jr. U.S. Pat. No. 3,514,634 shows single slope converter in which a voltage is converted to the duration of an output pulse. A reference voltage is converted into a linear ramp and the ramp compared with the analog input. The zero crossing, which varies with the unknown analog, is used to generate a flip-flop action that has an output that is time related to the unknown.
The above systems are generally complicated and involve the use of a substantial number of parts.